In the manufacture of cast multilayer films, it is desirable that the film layers adhere to each other. If the film layers adhere to each other, the need for a tie or an adhesive layer between the film layers is reduced; and thus, the multilayer film is more economical to produce. Further, if the layers of a multilayer film adhere more strongly to each other, the film is of a superior quality as it is stronger and the separate layers are less subject to peeling apart or delamination. Such a peeling apart or delamination particularly occurs after films or products therefrom are subjected to retorting or like conditions.
In the manufacture of multilayer films or coextrudates, the molten multilayer film exits an extruder and passes over at least one chill roll. In this process, it is believed that the higher the temperature of the chill roll, the better the adhesion between the layers of product. Even with this conventional wisdom, it is difficult to bond polyolefins to vinylidene chloride copolymers, polyesters, polyamides and/or polycarbonates.
It is believed that heretofore, it has not been proposed to decrease the chill roll temperature to obtain better adhesion between the layers of multilayer films.
It is therefore an object of this invention to provide blends from which film layers can be coextruded to form multilayer products It is a further object of this invention that said film layers have better adhesion to each other. It is also an object of this invention to provide a coextrusion process which produces films with layers which have better adhesion to each other.
In addition, it is an object of this invention to provide multilayer films which have better adhesion to each other and which maintain this desirable quality even after the rigors of retorting or like conditions.